ABSTRACT
Adenosine is a building block of RNA and many small biomolecules such as ATP and NADH, and at the same time it serves as a regulator of tissue function in practically every cell of the human body. The main source of adenosine is from degradation of adenine nucleotides
and, therefore, its regulatory functions are intricately linked to the energy balance of organs with a high energy demand. A large family of purinergic receptors may respond to ATP, ADP, and adenosine, and thereby orchestrate the respective metabolic requirements of a cell (Figure 1.1).
